Metal oxidation state effect in photoionization of gasphase metal halides

The full-valence photoelectron ~PE! spectrum of SnCl4 excited by synchrotron radiation in the ultraviolet ~UV! region is reported here for the first time, and compared with the analogous spectrum of SnCl2 previously published. Electron correlation effects in the different valence spectral regions are experimentally and theoretically analyzed for both tin chlorides. The theoretical results are obtained at ab initio 2h-1p CI level. Total-ion-yield ~TIY! spectra excited by synchrotron radiation are obtained for both molecules in the Sn 4d21 thresholds region for the first time. Sn 4d excited states in the two chlorides are hence identified through the resonant features displayed by the TIY spectra. The assignment is in good qualitative agreement with the excitation energies and oscillator strengths calculated at ab initio CI level. Clear differences exhibited by both PE and TIY spectra reported in this work originate from the different metal oxidation state in the two apparently similar chlorides, or equivalently, from the different involvement of the valence atomic orbitals of tin to form the chemical bonds of the molecule. Inner-valence ionizations in the investigated molecules are shown to be a sensitive probe of the halogen chemical environment, being related to the Sn-Cl bond polarization.